The clinical manifestation of autism spectrum disorder (ASD) is highly complex and heterogeneous, with medical and mental health disruptions beyond the three core behavioral criteria used for diagnosis (social behavior, communication, restricted interests/repetitive behavior). Co-occurring medical conditions, such as gastrointestinal dysfunction (GID), often are overlooked when designing research strategies to understand the mechanisms underlying the expression of ASD. The developmental mechanisms through which such diverse symptoms arise are unknown, but we hypothesize that some autism vulnerability genes encode pleiotropic molecules that participate in the development and function of multiple systems. This unique hypothesis is based on our discovery that the gene encoding the tyrosine kinase receptor MET carries a 5'common polymorphism (C) that disrupts transcription. In total, 6 independent cohorts from 3 different laboratories have identified this and one other variant (intron 1) that is enriched in ASD. MET plays a role in brain wiring and GI epithelial cell repair. Our recent retrospective study in 200+ AGRE families demonstrated that the C allele is represented in 65% of the cases with co-occurring GID and ASD, compared to 58% in ASD alone and 47% in the general population. This R21 initiative proposes a prospective study at Children's Hospital of Los Angeles/USC and the Monroe Carell Jr Children's Hospital at Vanderbilt University. In Aim 1, we will characterize GID in pediatric populations with and without ASD. The study population will be characterized in detail with both a standardized instrument for diagnosing functional GI disorders in children, the Questionnaire on Pediatric Gastrointestinal Symptoms, and with the clinical acumen of an experienced pediatric gastroenterologist. Nutritional information also will be collected to determine whether there are patterns of dysfunction that correlate with dietary and nutritional status. The in-depth characterization of GID in ASD will provide unique epidemiological descriptions of the study population that may reveal specific patterns of GI conditions within the +ASD/+GID group. In Aim 2, we will connect the genetic risk findings with biological changes that may account for GI and brain dysfunction. We will genotype all participants at the two ASD- associated MET loci. We also will quantify MET protein in the same study population in peripheral monocytes, which is the primary blood cell type that expresses MET. We have ascertained gut biopsies from an additional group of +ASD/+GID subjects and will utilize these tissues to directly measure pan-MET and phospho-MET protein levels. PUBLIC HEALTH RELEVANCE: The research proposal will directly investigate relationships between co-occurring medical conditions and ASD, testing a biological hypothesis regarding disruption of MET signaling as a common theme. The studies will provide insight into patient stratification and biomarker identity that may improve diagnosis and treatment.